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Gamma Ray Burst Visible At Record Distance
Invisible Pink Unicorn writes "A gamma ray burst detected on March 19 by NASA's Swift satellite has set a new record for the most distant object that could be seen with the naked eye. The burst had a measured redshift of 0.94, meaning the explosion took place 7.5 billion years ago. The optical afterglow from heated gas was 2.5 million times more luminous than the most luminous supernova ever recorded, making it the most intrinsically bright object ever observed by humans in the universe. The previous most distant object visible to the naked eye is the nearby galaxy M33, a relatively short 2.9 million light years from Earth."
You'd need a bit more than SPF-50 to deal with that one, though...
In Xanadu did Kubla Khan
A stately pleasure dome decree
For you newcomers, a record was like a mechanical CD but larger. The diameter of a CD is about half that of a Long Playing Record, so "Record Distance" is a distance comparable to the width of two CDs. I don't know why astronomers are the ones studying lights at that distance.
For anyone interested, here's the email that I received from the author:
Hi John,
Thanks for your message. I was the principle author of the press release, so I will try to answer your question. I should note that the press release was reviewed by numerous scientists. But it was edited at NASA headquarters before it was made public.
In my original draft, I purposefully avoided making the statement that the GRB was 7.5 billion light-years from Earth, because as your message implies, it is problematic to express specific distances when one is talking about events that happened in the very distant past, because the universe is rapidly expanding. Such is the case when trying to express a "distance" to GRB 080319B.
The most relevant direct "distance" measurement is the object's redshift, which was measured to be 0.94. As the press release explained, this measurement tells astronomers how much the GRB's light was "stretched" by cosmic expansion. I used this popular website from a renowned UCLA cosmologist to convert the object's redshift to a light-travel time:
http://www.astro.ucla.edu/~wright/CosmoCalc.html
When I entered the redshift and the cosmological parameters based on the latest results from the WMAP satellite and large-scale galaxy surveys, the calculator gave me a light-travel time of 7.5 billion years. In other words, the light from this GRB was emitted 7.5 billion years ago.
But at the time the burst occurred, Earth didn't even exist, so how does one express a "distance" between one object and another object that does not exist? In addition, 7.5 billion years ago, the visible universe was a much smaller place than it is now, because cosmic expansion has made the universe much bigger during those intervening 7.5 billion years. The GRB's host galaxy and the Milky Way Galaxy would have been much closer back then than they are today (please note that the Milky Way would have been a lot different back then, but it undoubtedly existed at that time). In fact, back then, the two galaxies would have been much closer than 7.5 billion light-years. And yet because of cosmic expansion, the two galaxies are currently much farther apart than 7.5 billion light-years. So there really is not an ideal way to express such a huge distance.
In my opinion, the best way to express such a huge distance in a rapidly expanding universe at the level of a popular audience is to express distances in terms of light-travel time, which is what I did in the original draft of the press release. And because our best current measurements suggest that the universe is 13.7 billion years old, an event taking place 7.5 billion years ago is roughly halfway across the visible universe. Some of the scientists at NASA probably felt that it was important to specify a distance in a unit of distance rather than in a unit of time, so they translated the light travel time to a distance in light-years. I realize this is imprecise from a strict scientific perspective, but the NASA scientists concluded that there is no better way to express it, and I cannot think of a better way to do it.
The problem, of course, is that the most precise way to express the distance is to state the redshift, which I did in the press release. Unfortunately, the term "redshift" has little meaning to the media and public, and the general public does not have the familiarity with astronomical terminology to be able to translate a redshift of 0.94 into a distance that has any deep meaning.
Best regards,
Robert Naeye, NASA Goddard Space Flight Center